I apologize in advance if this question is simple and I'm just completely missing it, but are these two mutually exclusive?

I know you can make Acrobatics check to move past enemies without provoking AoO's, so if you were to just get your Acrobatics skill high enough, would you even need the Mobility feat? Or do they function separately?

I played a Monk with Panther Style and a high acrobatics + Mobility. In essence, I would move past the enemy, provoking the AoO if they weren't too hard hitting, or using Acrobatics to prevent AoO, with Mobility as a back up if my dice luck was poor.

This build was pretty awesome, ripostes with Panther Style, Multiple AoO if the enemy provokes (and having me move into advantageous spots on the battle map to make it so they did just was bonus!) and then Acrobatics or Mobility to avoid damage myself.

The nice part was it helped with the whole "Monks never get to flurry if they move" argument, since I usually hit something 3-4 times a round in most cases.

It depends. If your GM uses monsters(not humanoids) they get larger past level 10 and their CMD jumps by a lot making it much harder to pass acrobatics checks. Of course if your AC is low enough that the exta +4 does not mean a lot then mobility won't matter that much anyway.